1. Field of the Invention
The present invention relates to an aberration correcting method, and an aberration correcting imaging apparatus.
2. Description of the Related Art
Studies are being advanced in the field of adaptive-optics scanning laser ophthalmoscope (AO-SLO) and adaptive-optics optical coherence tomography (AO-OCT), which incorporate adaptive optics (AO) functions in optical systems. Adaptive Optics, as applied to SLO and OCT, refers to techniques used to improve the performance optical systems which adapt to correct aberrations introduced during measuring of an eye. For example, an example of AO-OCT is described in “High-speed volumetric imaging of cone photoreceptors with adaptive optics spectral-domain optical coherence tomography” disclosed by Y. Zhang et al, Optics Express, Vol. 14, No. 10, 15 May 2006. AO-SLO and AO-OCT usually measure a wavefront of the eye using the Shack-Hartmann wavefront sensor. The Shack-Hartmann wavefront sensor method is a method for measuring a wavefront by inputting to be measured light to the eye, and receiving reflected light thereof at a CCD camera through a microlens array. AO-SLO and AO-OCT enable imaging at high resolution by driving a deformable mirror or space phase modulator so as to correct the measured wavefront, and performing imaging of the fundus via these.
In general, when the numerical aperture (NA) of an optical irradiation system is raised to acquire high resolution imaging, an aberration level also increases due to irregularities of optical tissue of the eye, such as the cornea, the crystalline lens, and so forth. Also, the aberration shape is complicated. Although several techniques for correcting this aberration with AO are known, the correction of high levels of aberration and aberration of a complicated shape requires performing aberration measurement at high resolution, and to drive a wavefront correction device at high resolution. A space phase modulator employing liquid crystal enables wavefront correction at such high resolution. A common space phase modulator used for AO can perform correction with resolution of around 600×800 pixels.
On the other hand, the number of lenses in a lens array of the Shack-Hartmann wavefront sensor generally used for AO is around 30×40. Resolution of aberration measurement is determined by this number of lens arrays, and accordingly, there are only 30×40 measurement points.
There are principally two methods to control an aberration corrector by acquiring aberration information from the Shack-Hartmann sensor. One method is to fit aberration to a Zernike polynomial function (Zernike polynomials), and control the aberration corrector according to the coefficients thereof (Zernike coefficients). The other method is to control the aberration corrector based on the wavefront phase at a given aberration measurement point.
In the case of the method of controlling the corrector using Zernike coefficients, the wavefront is expressed by the Zernike polynomial function that yields those coefficients, and accordingly, a control value according to resolution of the corrector can be calculated even when controlling a corrector having different resolution. In the case of the method of controlling the corrector using Zernike coefficients, the wavefront is expressed by the function, and accordingly, when there is disturbance from eyelashes, the eyelid, or the like, at the time of aberration measurement, normal fitting fails, and correction of the wavefront cannot be performed correctly.
On the other hand, in the case of the method of acquiring phase information, correct data can be acquired with regard to the point that the spots on the Shack-Hartmann sensor can be measured. Accordingly, control which is robust regarding disturbance is enabled.